Harriette Thompson participates in the Rock 'n' Roll San Diego marathon benefiting the Leukemia and Lymphoma Society on June 1 in San Diego. / Jerod Harris, Getty Images,

by Jolie Lee, USA TODAY Network

by Jolie Lee, USA TODAY Network

At age 91, Harriette Thompson of North Carolina set a record in Sunday's Rock 'n' Roll San Diego marathon.

With a time of seven hours, seven minutes and 42 seconds, Thompson broke the U.S. record for the fastest marathon run in the 90-94 age group, reported KNSD-TV in San Diego.

The previous record was held by a 90-year-old runner who finished a marathon in 8:53:08, KNSD reported.

Thompson also became the second-oldest marathon finisher in U.S. history - the oldest was 92 years old - Competitor.com reported.

Thompson started running marathons when she was 76 years old and has run one every year since. Sunday's race was Thompson's 15th marathon, Runner's World reported.

"You're never too old to do it," she told the magazine.

Thompson beat cancer of the palate in 1987. She has always run for the Leukemia and Lymphoma Society and Team In Training, raising more than $90,000 for the cause, according to Runner's World.

She's battling cancer again and just completed radiation on her legs before Sunday's race, KNSD said.

To train for the race, Thompson told the TV station, "I try to run around the block, and I do a few 5Ks. I think the most I've done this year is an 8K, so it's sort of a lot to ask to jump from that to 26 (miles)."

Thompson is a former concert pianist. To deal with the monotony of running, she mentally played old piano pieces she had performed, according to Competitor.com.